Vacuum chuck for clamping workpieces, measuring devices and method for checking workpieces, in particular wafers

ABSTRACT

A vacuum chuck for clamping workpieces, in particular wafers, and a measuring device and a method for checking workpieces by way of X-ray fluorescent radiation. The vacuum chuck has a clamping plate having a support surface, having at least one suction connection arranged on a base body for connecting to a negative-pressure device and for clamping the workpiece on the clamping plate by negative pressure received by the base body and having several suction grooves arranged in the clamping plate and are open towards the support surface. The support surface has concentric suction grooves having a suction opening to which a negative-pressure line is connected or which is connected to a work channel. Each suction groove having a separate negative pressure, which is separate to the adjacent suction groove, is selectively controlled by a control valve by a control for supplying the respective negative pressure in the respective suction groove.

This application claims priority of German Application No. 10 2016 101842.2 filed Feb. 3, 2016, which is hereby incorporated herein byreference.

The invention relates to a vacuum chuck for clamping workpieces, inparticular wafers, and a measuring device for checking workpiecesclamped by such a vacuum chuck and a method for checking a workpiececlamped on the vacuum chuck.

A vacuum chuck is known from DE 20 2013 102 800 U1 which comprises asupport or clamping surface for loading and clamping a workpiece bymeans of negative pressure. A clamping plate having the support andclamping surface is received by a base body which comprises a suctionconnection for connecting to a negative-pressure device for applying thenegative pressure in the suction opening. Such vacuum chucks have thedisadvantage that several suction openings aligned in parallel to oneanother are mutually supplied with negative pressure by anegative-pressure line, whereby an increased performance of thenegative-pressure device is required after the receiving and clamping ofsmaller workpieces.

A vacuum chuck for checking wafers is known from a press release by thecompany Horst Witte Gerätebau Barskamp KG in 21354 Bleckede from 2011.This vacuum chuck has a clamping surface made of a microporous material.Very thin workpieces are fixed by this microstructure in anon-level-dependent and damage-free manner. The clamping surface isdivided into three switchable clamping regions for wafers of differentsizes. This clamping plate consisting of a microporous material for avacuum chuck, however, has the disadvantage that it is very sensitiveduring handling and the clamping function is impaired when adding to ordisplacing the surface. Furthermore, this can only be used to a limitedextent. In addition, a high negative-pressure performance is alsorequired by the microporous surface of the clamping surface in order tofix the workpieces on the clamping surface, if these do not completelycover the selected segment.

The object of the invention is to propose a vacuum chuck for clampingworkpieces, in particular wafers, with which a simple and even clampingof the workpieces on a support surface of a clamping plate is enabled.Furthermore, the object of the invention is to propose a vacuum chuckfor a measuring device for checking workpieces and a method for checkingthese workpieces by means of X-ray fluorescent radiation.

This object is solved by a vacuum chuck in which each suction groove inthe support layer of the clamping plate having at least one separatenegative pressure, which is separate to the adjacent suction groove, isselectively controlled by means of at least one control valve by acontrol for the application of the negative pressure in the respectivesuction groove. By doing so, corresponding control of the respectivesuction groove covered by the workpiece or covered suction grooves takesplace depending on the size of the workpiece to be clamped, whereby ahigh degree of effectiveness or a reduced performance of anegative-pressure device are required in order to enable a secureclamping of the workpiece.

Preferably, the support surface has several concentric suction grooveshaving at least one suction opening, to which the negative-pressure lineis connected or which is connected to a work channel. Particularly inthe case of wafers, which have a circular shape, a suction groovecorrespondingly adjusted to the size is provided near to the outer edgeregion of the wafer by the circularly formed suction grooves. Thisenables a secure clamping. Thus, further suction grooves that are largerin diameter do not need to be supplied with negative pressure. Thus,energy can be successfully saved.

The vacuum chuck can preferably have a base plate made of a material forchecking the workpieces, in particular wafers, by means of X-rayfluorescent radiation, the atomic number of said base plate beingselected in such a way that, with primary radiation of an X-rayfluorescent measuring device aimed at the workpiece, a small amount ofscattered radiation is produced and the energy of the fluorescentradiation is so small that it is absorbed into the material of theobject being checked. Thus, a complete or almost complete absorption isadvantageously provided.

Alternatively, the base plate can be selected from a material in whichthe atomic number is chosen in such a way that the primary X-rayradiation aimed at the workpiece produces a fluorescent radiation, inwhich in a range of 20% to 80% of the fluorescent radiation is absorbedinto the material of the workpiece to be checked. Thus, the fluorescentradiation that is not absorbed can be used for evaluation when detectingthe measuring signals using a detector.

A further preferred embodiment of the vacuum chuck provides that atleast three lifting pins are provided in the base plate, which aremoveable from a retracted position in or below the support surface ofthe clamping plate into an extended position. This enables, for example,the workpiece to be fitted onto the lifting pin at the beginning of thechecking process, in particular by a handling device. Subsequently, theworkpiece, after removing the handling device from the region of thelifting pins, can be gently positioned and placed on the support surfaceof the clamping plate by means of the lifting pins, in order tosubsequently tension this workpiece. In the same way, gently raising theworkpiece from the support surface by the lifting pins can take placeafter the checking in order to subsequently enable a manual removal oran automatic removal.

The lifting pins preferably have a support surface that is similar to asuction cup or a receiving element having a central hole, which isconnected to a negative-pressure line or a suction channel by means ofnegative pressure for producing a holding force. This receiving elementis preferably formed from an elastomer in order to, on the one hand,avoid scratching the workpiece and, on the other hand, to enable a quickconstruction of a vacuum for fixing the workpiece on the lifting pinswhen applying negative pressure.

The lifting pins are preferably able to be transferred into theretracted and extended positions by a moveable sliding carriage that isarranged in the base body, wherein a work cylinder, in particular apneumatic cylinder, controls the shifting movement of the slidingcarriage. Thus, a vacuum chuck of such a flat construction can beproduced, since the shifting movement of the sliding carriage takesplace in an XY-plane, whereas the extending movement of the lifting pinsis provided in a perpendicular axis, in particular a Z-axis. Inaddition, the negative-pressure device can, at the same time, also serveto control the work cylinder.

The moveable sliding carriage advantageously has a slanting controlsurface, along which at least one control element, in particular a camor a friction or antifriction bearing element is guided, which is fixedon the lifting pin and moves this. Thus, the shifting movement of thesliding carriage can be directly transferred into a lifting movement ofthe lifting pins.

Furthermore, the lifting pin is preferably guided along a guiding sleevesuch that it is able to be shifted, said guiding sleeve being connectedto a negative-pressure line or the suction channel in the base body.Thus, a telescope-like construction for the lifting pin is provided,whereby a flat construction of the vacuum chuck can furthermore beachieved. The guiding sleeve is preferably firmly fixed on the basebody, and its inner hole ends in the suction channel.

The moveable sliding carriage is preferably positioned in the base bodybetween the clamping plate lying on the base body and an underplateprovided on the underside of the base body. This sliding carriage can beglidingly guided between the clamping plate and the underplate, or bymeans of rollers or balls. Alternatively, the sliding carriage can beheld moveably along by guiding elements that are fixed in the base body.

The moveable sliding carriage is preferably provided in the base body ina receiving space on which sensor elements are provided on two endregions opposing each other, said sensor elements detecting theretracted or extended position of the lifting pins depending on theposition of the sliding carriage in the receiving space. Thus,monitoring an automatic control of such a vacuum chuck is enabled.

Furthermore, several stopping pins are preferably provided in the basebody, said stopping pins being moveable from a retracted position in orbelow the support surface of the clamping plate into an extended stopposition. These stopping pins are used in particular when manuallyfitting the vacuum chuck with a workpiece, in particular a wafer. Ifthese are not necessary, as is particularly the case with automaticallyfitting, they can be positioned in or below the support surface of theclamping plate.

The one or more stopping pins are preferably supplied with positivepressure for transferring into the extended stop position. To do so, asupply channel is advantageously provided in each case for the one ormore stopping pins, the positive pressure being supplied in said supplychannel. Thus, two or more stopping pins, which are provided for adegree of clamping of the workpiece, can be controlled at the same time.

Furthermore, the stopping pins independently adopt the retractedposition by venting the supply channel by means of a return springtouching the stopping pin. Thus, it is ensured that, even when adisruption of the pressure supply takes place, the stopping pins do notprotrude with respect to the clamping surface of the clamping plate andthus the vacuum chuck can be further used.

Preferably, at least two stopping pins are allocated to every suctiongroove, said stopping pins being able to be controlled by a commonsupply channel with positive pressure, wherein these at least twostopping pins are, in each case, arranged radially outside therespective suction groove, which is controlled at least for thecorresponding size of the workpiece to be received. Thus, thecorresponding stopping pins are allocated to every size of the suctiongroove such that this vacuum chuck is able to be used for several sizesof workpieces. For example, wafers having a diameter of 4″, 6″, 8″, 10″and/or 12″ (inches) can be clamped and checked.

A further advantageous embodiment of the vacuum chuck provides that atleast three lifting pins are provided outside a smallest or a firstsuction groove and, offset relative to these lifting pins seen from theperipheral direction, at least two stopping pins are allocated to thesmallest or first suction groove. Thus, all sizes of workpieces to bereceived for the vacuum chuck are received equally by the lifting pins,lowered onto the support surface and/or lifted up again and similarly,manual fitting is possible because of the positioning of the workpieceon the respective stopping pins.

A further preferred embodiment of the vacuum chuck provides that atleast two stopping pins are provided between two adjacent furthersuction grooves, in each case. The stopping pins arranged in therespective suction groove are preferably aligned in a radial directionalong a straight line. Thus, the same handling requirements can be givenfor different sizes of workpieces to be received on the clamping plateof the vacuum chuck.

The base body of the vacuum chuck preferably has work channels runningcomplementarily relative to the suction grooves, on a side pointingtowards the clamping plate, said work channels being connected to atleast one suction opening of the respective suction groove in thesupport surface relative to the clamping plate, and preferably everywork channel is controlled separately with a vacuum by a control valve.Thus, an arrangement of such a flat construction and selective controlof the respective suction groove are achieved.

In each case, a supply channel is preferably provided in an underplateof the vacuum chuck, said supply channel being connected to a respectivefeed channel in the base plate, wherein the supply channel supplies atleast two lifting pins with positive pressure at the same time. Thissimilarly enables a compact arrangement of the vacuum chuck with a smallconstruction height.

The object of the invention is furthermore solved by a measuring devicefor checking workpieces, in particular wafers, with X-ray fluorescentradiation, in which a vacuum chuck according to one of the embodimentsdescribed above is provided on a moveable measuring table of themeasuring device. Because of the small construction height, such avacuum chuck can be used in existing X-ray fluorescent measuringdevices. Furthermore, a simple adjustment to different measuring objectsand materials of the workpieces to be checked can be enabled because ofthe selection of the material for the base plate. Thus, correspondingvacuum chucks can be exchanged or the clamping plates can be able to beexchanged with a different material and are able to be fixed to the basebody of the vacuum chuck.

The object of the invention is further solved by a method for checking aworkpiece, in particular a wafer, with X-ray fluorescent radiation, inwhich the following steps are provided in particular:

The vacuum chuck is activated by a workpiece before fitting. Thus,lifting pins are transferred into an extended position with respect tothe support surface of the clamping plate. Subsequently, the workpieceto be checked can be placed on the lifting pins by a handling device anda negative pressure can be applied to the lifting pins in order to fixthe workpiece to be checked to the lifting pins. Subsequently, thehandling device can be guided out of the measuring device. The liftingpins are controlled by a shifting movement such that these aretransferred into a retracted position and the workpiece is placed on thesupport surface. Then at least the outermost suction groove is suppliedwith negative pressure corresponding to the size of the workpiece andthe workpiece is clamped on the support surface. After the workpiece hasbeen checked by means of X-ray fluorescent radiation, the negativepressure is shut off by the at least one suction groove supplied withit, and the lifting pins are transferred into the extended position.Subsequently, the workpiece is grasped by the handling device and thenegative pressure on the lifting pins is shut off. The workpiece canthen be removed from the measuring device by means of the handlingdevice.

Preferably, the negative pressure applied to the lifting pins can alsobe retained on the support surface of the clamping plate during theclamping of the workpiece. Alternatively, it can also be switched off atthe point in time of clamping the workpiece on the support surface.

The invention and further advantageous embodiments and developments ofthe same are described and explained below in more detail by means ofexamples presented in the drawings. The features that can be ascertainedfrom the description and the drawings can be applied individually ortogether in any combination according to the invention. Here are shown:

FIG. 1 a perspective view of an X-ray fluorescent measuring devicehaving a vacuum chuck,

FIG. 2 a schematic view from above of the vacuum chuck according to FIG.1,

FIG. 3 a schematic sectional view of the vacuum chuck along line II-IIin FIG. 2,

FIG. 4 a schematically enlarged view of detail B in FIG. 3,

FIG. 5 a schematically enlarged view of detail C in FIG. 3,

FIG. 6 a perspective view of the vacuum chuck with a raised clampingplate,

FIG. 7 a schematic view from above of the base body of the vacuum chuck,

FIG. 8 a schematic view from below of the base body of the vacuum chuckwith a raised underplate,

FIG. 9 a perspective detailed view of detail D in FIG. 3,

FIG. 10 a schematically enlarged view of a lifting pin according todetail D in FIG. 3,

FIG. 11 a schematic sectional view along line XI-XI in FIG. 9,

FIG. 12 a schematic view from below of an underplate of the base body ofthe vacuum chuck with a raised covering plate,

FIG. 13 a schematic sectional view along line XII-XII in FIG. 12,

FIG. 14 a perspective view of the vacuum chuck in a working positionduring an automatic fitting with a workpiece,

FIG. 15 a perspective view of a vacuum chuck with a received workpiece,

FIG. 16 a perspective view of a working position of the vacuum chuck formanually fitting a workpiece, and

FIG. 17 a perspective view of a manually fitted workpiece on the vacuumchuck.

A measuring device 11 for carrying out a measurement by means of X-rayfluorescent radiation is depicted perspectively in FIG. 1. Thismeasuring device 11 comprises a measuring table 12 which is moveable,for example, in an XY plane by means of a linear axis system 14. Aradiation source for producing primary radiation and one or morediverting elements for guiding the primary X-ray radiation onto aworkpiece 19 lying on the measuring table 12, which are not depicted inmore detail, are inside a housing 16 of the measuring device 11.Furthermore, the measuring device 11 in the housing 16 comprises adetector, by means of which the secondary radiation that is limited bythe workpiece 19 is detected. This detector is connected to a controldevice 17 in order to evaluate the detected measuring signals andadvantageously display them via a display.

A vacuum chuck 18 according to the invention, which is described in moredetail in the figures below, serves to receive and clamp workpieces 19,in particular wafers. This vacuum chuck 18 can be mounted or fixed onthe measuring table 12 of the measuring device 11 in order to fix theworkpiece 19, in particular the wafer, for checking, for example bymeans of X-ray fluorescent radiation. This workpiece 19 can be placed onthe vacuum chuck 18 by a handling device 89, for example.

In FIG. 2, a schematic view from above of the vacuum chuck 18 isdepicted. This comprises a clamping plate 21 having a support surface 27which comprises several suction grooves 22, 23, 24, 25, 26. Thesesuction grooves 22 to 26 are formed by a circular indentation which isintroduced into the support surface 27 of the clamping plate 21.Preferably, the suction grooves 22 to 26 are arranged concentricallyrelative to one another. The number of suction grooves 22 to 26 can beadjusted for the measuring object depending on the size of the clampingplate 21 and/or the workpiece 19 to be received.

Furthermore, the vacuum chuck 18 comprises lifting pins 29, for examplethree lifting pins 29. These are preferably arranged between the firstsuction groove 22 and the second suction groove 23. In particular, theseare arranged to be evenly distributed across the periphery. The liftingpins 29 are preferably made from precious metal.

The vacuum chuck 18 can furthermore have stopping pins 31, wherein atleast two stopping pins 31 can be allocated to every suction groove 22to 26 in order to achieve positioning and alignment of the workpiece 19.The stopping pins 31 are arranged to be offset with respect to oneanother, for example, in particular offset with respect to one anotherat an angle of 90°. For two smaller sizes of workpieces 19 to bereceived, three stopping pins 31 are, for example, allocated to thefirst suction groove 22 and the second suction groove 22 in each case,wherein two stopping pins 31 lie on a common straight line in order toobtain additional alignment on a stopping surface of the workpiece 19.

The vacuum chuck 18 comprises a base body 33 which receives the clampingplate 21. The clamping surface 21 can be provided to be fixed on thebase body, for example by adhesion, screwing or riveting. Alternatively,the clamping plate 21 can also be provided exchangeably on the base body33. To do this, detachable fixing elements are preferably provided. Theclamping plate 21 can consist of different materials and be selectedaccording to the measuring object.

An actuator 34 is provided on a front face of the vacuum chuck 18, saidactuator controlling a multi-position valve that is not depicted in moredetail, in order to correspondingly activate the individual stoppingpins 31 according to the size of the workpieces 19 to be clamped. Thisis described in more detail below. Several connections 43 are providedunder a covering 32, said connections being discussed by means of FIGS.7 and 8 below.

In FIG. 3, a schematic sectional view along the line II-II in FIG. 2 isdepicted. The construction in principle of the vacuum chuck 18 emergesfrom this. The clamping plate 21 is on an upper side of the base body33. An underplate 36 is fixed on an underside of the base body 33. Workchannels 37, 38, 39, 40, 41 (FIG. 6) for controlling the suction grooves22 to 26 are located between the clamping plate 21 and the base body 33.These work channels 37 to 41 are, by way of example, depicted enlargedin cross-section in FIG. 4, and in a perspective view from above in FIG.6, wherein FIG. 6 depicts a perspective view of the base body 33 in thecase of a removed clamping plate 21. The work channels 37 to 41 arepreferably introduced into the surface of the base body 33.Alternatively, these can also be introduced into the underside of theclamping plate 21. The suction grooves 22 to 26 are provided on theupper side of the clamping plate 21. These are formed to be rectangular,for example, and extend only slightly from the support surface 27 in thedirection of the base body 33. At least one suction opening 35 isrespectively provided at least between each work channel 37 to 41 andeach suction groove 22 to 26 that is allocated to the work channel 37 to41 to connect the suction grooves 22 to 26 to the work channels 37 to41. This detail B according to FIG. 3 is depicted enlarged in FIG. 4.

Detail C in FIG. 3 is depicted schematically enlarged in FIG. 5, whereinthe stopping pins 31 are depicted in a retracted position in FIG. 3 andenlarged in an extended position in FIG. 5. The stopping pin 31 isreceived in a receiver 53 in the base body 33, wherein the stopping pin31 is inserted into a piston 54. The piston 54 is shiftably guided inthe receiver 53. A return spring 55 is arranged between the stopping pin31 and the piston 51. This ensures that, when the pressure surface 56 onthe stopping pin 31 is not supplied with positive pressure, the stoppingpin 31 is transferred into a retracted position. Thus, a front face 57of the stopping pin 31 is in the support surface 27 of the clampingplate 21 or below. The receiver 54 is supplied with positive pressure toproduce and maintain an extending movement of the stopping pin 31, saidpositive pressure acting on the pressure surface 56. A blow-out throughan opening in the base body 33 and in the clamping plate 21 is preventedby a gasket 58, the stopping pin 31 extending through said opening. Asupply channel 48 for the positive pressure is sealed with respect toadjacent supply channels 49, 50, 51 (FIG. 7) by a sealing mat 61 whichis fixed to the base body 33 by means of an intermediary plate 62 byclamping. The stopping pin 31 is preferably produced from preciousmetal.

A perspective view of the base body 33 in a removed clamping plate 21 isdepicted in FIG. 6. From this, the courses of the individual workchannels 37, 38, 39, 40, 41 are able to be seen, which extend below thesuction grooves 22 to 26. By introducing the work channels 37 to 41 intothe base plate 33, a flat construction can be created in order to supplythe suction grooves 22 to 26 with negative pressure.

It can be seen in FIG. 7 that one connection hole 42, 42.1, 42.2, 42.3,42.4 and 42.5 is allocated to every work channel 37 to 41, saidconnection hole respectively leading to a connection piece 43, to whicha negative-pressure line is respectively able to be connected.Alternatively, the connection holes 42.4 and 42.5 can lead to aconnection piece 43. Each of these connection pieces 43 is separatelyconnected to a control valve 91, 92, 93, 94 and is separately controlledby this control valve 91 to 94. A control 96 is provided to controlthese control valves 91 to 94. Each of these control valves 91 to 94 isseparately controlled by the control 96. This control 96 can beconnected to the control device 17. The work channels 37 to 41 aresupplied with negative pressure by a negative-pressure device 97.

Furthermore, a connection piece 43 is provided on the base body 33,which is controlled by the control valve 95. This control valve 95regulates the applying of the negative pressure to the lifting pins 29.This is described in more detail in FIG. 13. This control valve 95 isalso switched by the control.

Furthermore, on an upper side of the base body 33, four feed channels 44to 47 are provided, through which, respectively, a positive pressure canbe guided into a supply channel 48 to 51 connected thereto. These supplychannels 48 to 51 can be controlled by the multi-switch valve which isselected by means of the operating element 34. These supply channels 48to 51 are supplied with positive pressure by a positive pressure device.This can be carried out by a separate positive pressure device or evenby correspondingly controlling the negative-pressure device 97.

At least two stopping pins 31 are allocated to every supply channel 48to 51. For example, the feed channel 44 ends in the supply channel 48,in which in total three stopping pins 31, for example, can becontrolled, which are arranged between the first suction groove 22 andthe second suction groove 23 or the corresponding work channel 37, 38.This feed channel 44 is supplied with compressed air, for example, if aworkpiece 19, in particular a wafer, with a diameter of 4″ (4 inches) isto be placed and clamped. The feed channel 45 is supplied for a 6″wafer, the feed channel 46 for an 8″ wafer and the feed channel 47 for a12″ wafer.

The course of the feed channels 44 to 47 and supply lines 48 to 51 arealso clear from the view of the base body 33 from below according toFIG. 8.

In the region of the feed channels 44 to 47, the work channels 39 to 41in the base body 33 are indeed interrupted; however, applying a vacuumin these regions is sufficient to obtain a circular vacuum in each caseinside the corresponding suction grooves 22 to 26, whereby a flatsupport of the workpiece 19 on the support surface 27 of the clampingplate 21 is provided.

A receiving space 64 in the base body 33 arises from FIG. 7 as well asFIG. 8, in which a moveable sliding carriage 65 is arranged, as isdepicted in particular in FIG. 8. This sliding carriage 65 receives thethree lifting pins 29. By means of a shifting movement of the slidingcarriage 65, which is controlled by a cylinder 66, in particular apneumatic cylinder, the lifting pins 29 are transferred from a retractedposition into an extended position. A connection 68 is connected to aconnection 69 on the cylinder 66 to control the cylinder 66. Theconnections 71 and 72 are connected to each other to control an opposingshifting movement. These connections 68, 71 are in each case controlledby a control with a control valve 98, 99 or by a common control valvecorresponding to the desired shifting movement. The cylinder 66 issupplied with positive pressure via a pressure device 100.

The supply and waste air of the cylinder 66 is regulated via the controlvalves 98, 99. The cylinder 66 can have an adjustable end positiondamping. Thus, a gentle lifting and lowering of the lifting pins 29 forplacing and lifting the workpiece 19 on the support surface 27 of theclamping plate 21 can be adjusted and enabled. The connections 68, 69,by means of which the control valves 98, 99 are connected in the vacuumchuck 18 in order to supply the supply air for the cylinder 66, compriseone-way-restrictors in order to restrict at least the waste air.

Sensor elements 67 are arranged opposite one another to detect theposition of the respective retracted or extended position of the liftingpins 29. These detect the position of the sliding carriage 65 in thereceiving space 64 and convey the signals to the control 96 and/or thecontrol device 17. The position of the lifting pins 29 is also detectedfrom the position of the sliding carriage 65 because of the forcedguiding of the lifting pins 29.

A perspective view of the sliding carriage 65 with the lifting pins 29is depicted in FIG. 9. FIG. 10 shows a first sectional view of thelifting pins 29. FIG. 11 shows a further sectional view along the lineXI-XI in FIG. 9.

The sliding carriage 65 is preferably approximately H-shaped, whereinlongitudinal indentations 74 are provided in a leg, the lifting pins 29being moveable inside said indentations. The lifting pin 29 is connectedto at least one control element 75, in particular a cam, a friction oranti-friction bearing, which is moveable along a slanted control surface76. A shifting movement of the sliding carriage 65 in an XY-plane oraccording to arrow 77 produces an extending and retracting movement ofthe lifting pins 29 which is aligned perpendicular to said plane. Thus,the lifting pin 29 is guided to be vertically moveable along a guidingsleeve 78 such that this is able to be transferred from a retractedposition into an extended position that is depicted in FIG. 10 and FIG.11. All three lifting pins 29 are able to be moved up and down at thesame time by the shifting movement of the sliding carriage 65.

On its upper end, the lifting pin 29 has a receiving element 81 that issimilar to a suction cup, which is preferably formed from plastic. Ahole 82 is provided inside the receiving element 81, said hole aligningwith the guiding sleeve 78 such that a negative pressure produced by theguiding sleeve 78 also abuts on the receiving element 81. With asupporting workpiece 19, this is fixed to the support element 81. Theguiding sleeve 78 and the lifting pins 29 are connected to one anotherby a common suction channel 84. Such a suction channel 84 is illustratedin the view from below of the underplate 36 in FIG. 12. The branchesdepicted there show that a connection to the respective guiding sleeve78 is provided on the respective ends of the suction channel 84. Anegative pressure is produced in the suction channel 84 by anegative-pressure device 97, for example, via a connection hole 85 and abranch channel 86. Applying and switching off the vacuum is regulated bythe control 96 and the control valve 95. The work channel 84 ispreferably introduced into the underplate 36 and this is in turn sealedwith a separate covering plate 87.

Taking FIG. 1 and FIGS. 14 and 15 into account, an automatic fitting andchecking of a workpiece 19 is described below.

The workpiece 19 is grasped by a handling device 89 according to FIG. 1from a magazine not depicted in more detail or a feed device and issupplied to the measuring device 11. The sliding carriage 65 is moved inthe vacuum chuck 18 by the cylinder 66 such that the lifting pins 29 aretransferred from a retracted position into the extended positiondepicted in FIG. 14. This extended position is also depicted in FIG. 10,for example. Subsequently, the workpiece 19 is placed, preferably in anexact position, on the receiving elements 81 of the lifting pins 29 bymeans of the handling device 89. Subsequently, a negative pressure isapplied to the lifting pins 29 such that the workpiece 19 is fixed tothe lifting pins 29 because of the vacuum. Subsequently, the handlingdevice 89 is guided out of the measuring device 11.

Subsequently, the cylinder 66 is controlled again in order to transferthe sliding carriage 65 into a further position, such that the liftingpins 29 are lowered and retracted. This can take place by at least oneof the control valves 98, 99 and be monitored by the sensor elements 67.The workpiece 19 comes to rest gently on the support surface 27 of theclamping plate 21. Before or during, if appropriate also after lowering,the respectively provided suction groove 22 to 26 is supplied with avacuum corresponding to the size of the workpiece 19, such that theworkpiece 19 is fixed to the clamping plate 21. The workpiece 19,according to FIG. 15, is an 8″ wafer, for example. At this point, whenthe workpiece 19 is fixed to the clamping plate 21, the negativepressure in the lifting pins 29 can be shut off by the control 96. Thiscan also further remain constant. Subsequently, checking and/ormeasuring the workpiece 19 takes place by means of X-ray fluorescentradiation. After finishing checking and/or measuring, the vacuum in thecorresponding suction groove 22 to 26 is released and, if the vacuum inthe lifting pins 29 has been switched off, this is activated again andswitched on before releasing the vacuum in the suction groove 22 to 26.A shifting movement of the sliding carriage 65 follows on from this suchthat the workpiece 19 is again lifted with respect to the supportsurface 27. Subsequently, the handling device 89 is again retracted intothe measuring device 11. In particular, this reaches under the workpiece19. After switching off the vacuum on the lifting pins 29, the workpiece19 can be guided out of the measuring device 11 and stacked or fed forfurther processing.

At least the suction groove 24 is supplied with a vacuum. Preferably,the smaller suction grooves 23 and/or 22 are also supplied with avacuum. The suction grooves 25 and 26 are thus not supplied with avacuum since these are not covered by the workpiece 19.

The positioning and placing of a workpiece by hand, i.e. a manualoperation, is described by FIGS. 16 and 17. To check a workpiece 19according to FIG. 17, which is a 4″ wafer for example, the operatingelement 34 is initially adjusted to 4″. Then the feed channel 44 and thesupply channel 48 are supplied with compressed air via the multi-switchvalve, whereby the stopping pins 31.1, 31.2, 31.3 allocated to thesuction groove 22 are extended. Subsequently, the workpiece 19 can beplaced on the two adjacently allocated stopping pins 31.1 and 31.2 withits flat section 20 and aligned with the third stopping pin 31.3. At thesame time as extending the stopping pins 31, a vacuum can be produced inthe suction groove 22. This can, however, also only take place afterplacing the workpiece 19 and its alignment with respect to the stoppingpins 31.1, 31.2, 31.3. To remove the workpiece 19, the vacuum isinitially switched off in the corresponding suction groove 22 to 26, insuction groove 22 in the exemplary embodiment. Then the workpiece 19 canby manually removed. Alternatively, there is the possibility of thelifting pins 29 being controlled in order to lift the workpiece 19 withrespect to the support surface 27 in order to enable an easier removal.

The invention claimed is:
 1. A vacuum chuck for clamping workpieces,having a clamping plate having a support surface, having at least onesuction connection arranged on a base body for connecting to anegative-pressure device and for clamping the workpiece on the clampingplate by way of negative pressure which is received by the base body andhaving several suction grooves arranged in the clamping plate and areopen towards the support surface, the support surface has severalconcentric suction grooves having at least one suction opening to whicha negative-pressure line is connected or which is connected to a workchannel, wherein every suction groove having a separate negativepressure, which is separate to the adjacent suction groove, isselectively controlled by way of at least one control valve by a controlfor supplying the respective negative pressure in the respective suctiongroove; wherein lifting pins are provided in the base body, the liftingpins being moveable between a retracted position, in which the liftingpins are in or below the support surface of the clamping plate, and anextended position, in which the lifting pins extend above the supportsurface, and wherein the lifting pins each have a receiving elementwhich comprises a central hole that is connected to a suction channel toproduce a holding force at the receiving element by way of negativepressure.
 2. The vacuum chuck according to claim 1, wherein a moveablesliding carriage is provided in the base body for controlling theretractable or the extendable position of the lifting pins, and fortransferring the lifting pins into the retracted position and into theextended position, the moveable sliding carriage having slanted controlsurfaces, along which at least one control element is guided such thatit is moveable, said control element being connected to the lifting pin.3. The vacuum chuck according to claim 1, wherein each of the liftingpins is guided along a guiding sleeve such that each lifting pin isshiftable, said guiding sleeve being connected to the suction channel inthe base body for producing a negative pressure.
 4. The vacuum chuckaccording to claim 1, wherein a moveable sliding carriage is positionedin the base body between the clamping plate lying on the base body andan underplate arranged on the underside of the base body.
 5. The vacuumchuck according to claim 1, wherein a moveable sliding carriage isarranged in a receiving space of the base body and two opposing sensorelements are allocated to the receiving space, whereby the adoption ofthe retracted or extended position of the lifting pins is detectabledepending on the position of the sliding carriage in the receivingspace.
 6. The vacuum chuck according to claim 1, further comprisingseveral stopping pins provided in the base body, which said stoppingpins are moveable from a retracted position in or below the supportsurface into an extended position above the support surface of theclamping plate.
 7. The vacuum chuck according to claim 6, wherein one ormore stopping pins for transferring into an extended stopping positionare connected to at least one supply channel which is supplied withpositive pressure and the stopping pins independently adopt theretracted position by venting the respective supply channel that isconnected to the at least one stopping pin and by way of a return springtouching the stopping pin.
 8. The vacuum chuck according to claim 6,wherein at least two stopping pins are allocated to every suctiongroove, said stopping pins configured to be controlled by positivepressure by one common supply channel.
 9. The vacuum chuck according toclaim 1, wherein three lifting pins are provided outside the smallest orfirst suction groove, and at least two stopping pins are provided offsetrelative to the three lifting pins.
 10. The vacuum chuck according toclaim 6, wherein at least two stopping pins are provided between twosuction grooves, wherein at least one of the at least two stopping pinsis adjacent to one of the two suction grooves.
 11. The vacuum chuckaccording to claim 1, wherein work channels that run complementarily tothe suction grooves are provided on a side of the base body pointingtowards the clamping plate, said work channels being connected to the atleast one suction opening with the suction grooves in the supportsurface of the clamping plate and every work channel is controlledseparately by vacuum by a control valve.
 12. The vacuum chuck accordingto claim 7, wherein supply channels are provided in an underplate, saidsupply channels being respectively connected to a feed channel, throughwhich the at least two stopping pins, which are allocated to the size ofthe workpiece, are simultaneously supplied with positive pressure. 13.The vacuum chuck according to claim 1, wherein the vacuum chuck isconfigured to clamp wafers.
 14. A measuring device for checkingworkpieces having X-ray fluorescent radiation, the measuring devicehaving a moveable measuring table for receiving the at least oneworkpiece, wherein a primary X-ray radiation produced by a radiationsource is aimed at the at least one workpiece, and emitted secondaryradiation is detected by a detector, and measuring signals detected bythe detector are evaluated by way of a control device, wherein thevacuum chuck according to claim 1 is provided on the moveable measuringtable.
 15. A method for checking a workpiece, with a measuring devicehaving X-ray fluorescent radiation, the measuring device having amoveable measuring table for receiving the workpiece, wherein a primaryX-ray radiation produced by a radiation source is aimed at theworkpiece, and emitted secondary radiation is detected by a detector,and measuring signals detected by the detector are evaluated by way of acontrol device, wherein a vacuum chuck is provided on the moveablemeasuring table, the vacuum chuck having a clamping plate having asupport surface, having at least one suction connection arranged on abase body for connecting to a negative-pressure device and for clampingthe workpiece on the clamping plate by way of negative pressure which isreceived by the base body and having several suction grooves arranged inthe clamping plate and are open towards the support surface, the supportsurface has several concentric suction grooves having at least onesuction opening to which a negative-pressure line is connected or whichis connected to a work channel, wherein every suction groove has aseparate negative pressure, which is separate to the adjacent suctiongroove, is selectively controlled by way of at least one control valveby a control for supplying the respective negative pressure in therespective suction groove, and wherein lifting pins are providedopposite the support surface of the clamping plate, the methodcomprising: before fitting the vacuum chuck with the workpiece, thelifting pins opposite the support surface of the clamping plate aretransferred into an extended position, placing the workpiece to bechecked on the lifting pins by a handling device, supplying the liftingpins with negative pressure and the workpiece to be checked is fixed tothem, transferring the lifting pins into a retracted position and theworkpiece is placed on the support surface, selecting at least one ofthe sizes of the workpiece in the control, which causes the control tosupply the corresponding suction groove with negative pressure and theworkpiece is fixed on the support surface, checking the workpiece by wayof X-ray fluorescent radiation, switching off the negative pressure inthe at least one suction groove, transferring the lifting pins into theextended position, grasping the workpiece by the handling device, andswitching off the negative pressure applied to the lifting pins andguiding the workpiece out of the measuring device by the handlingdevice.
 16. The method according to claim 15, wherein the negativepressure applied to the lifting pins is retained during the clamping ofthe workpiece on the support surface of the clamping plate.
 17. Themethod according to claim 15, wherein the negative pressure applied tothe lifting pins is switched off after transferring into a retractedposition and clamping the workpiece by the at least one suction groovesupplied with negative pressure and negative pressure is supplied to thelifting pins to lift the workpiece, before the negative pressure on theat least one suction groove is switched off for lifting the workpiece.